Automatic pilot



P. A. NOXON ET AL Nov. 27, 1956 AUTOMATIC PILOT :zaxuzonmuooaz 7 2 w .mwM m mm nur 1 i F l Q, s@ Qs NNN n mm

United States Patent O AUTOMATIC PILOT Paul A. Noxon, Tenafly, and AlanM. MacCallum, Maywood, N. J., assignors to Bendix Aviation Corporation,Teterboro, N. J., a corporation of Delaware Original application May 27,1944, Serial No. 537,952. Divided and this application October 21, 1949,Serial No. 122,792.

5 Claims. (Cl. 244-77) The present invention relates to an automaticnavigational control system adapted for use with drigible craft andconstitutes a division of application Serial No. 537,952, tiled May 29,1944.

Control systems of this general nature which have been heretoforeutilized have relied principally upon either pneumatic or hydraulicpressures, or a combination of both, for energizing the servomotors ofvarious control surfaces. As a result, known systems possessed certaindrawbacks, one being that where widely Varying altitudes were traversed,the wide kchange in `air densities aiected the reliability of pneumaticsystems while eXtreme changes in temperatures produced undesirableeffects on hydraulic systems. Moreover, the numerous conduits requiredin such pressure systems were particularly vulnerable to gun tire wherethe systems were used on war craft.

An object of the present invention, therefore, is to provide a novel andimproved automatic navigational coutrol system with the use of which theforegoing disadvantages are overcome.

Another object of the present invention is to provide a novel allelectric automatic pilot for aircraft of all sizes and uses wherebyoutstanding ease of control and complete maneuverability are obtained.The advantages of an all electric automatic pilot will be obvious. Forexample, the operation of such a system will not be hindered by highaltitude flight or by ilight through dust laden atmospheres. Moreover,the various electrical units constituting the pilot of the presentinvention are, to a certain extent, self-heating so that no diculty isencountered in operation at low temperatures.

A further object of the invention is to provide a novel automatic pilotin which the displacement signals for each axis of control are derivedfrom a common electrical instrument and transmitted to operate electricservolmotors of related control surfaces so that a rapid response on thepart of the control surfaces is obtained.

Another and further object is to provide a novel automatic pilot inwhich the various displacement signals may be readily addedalgebraically thereby making possible the free use of derivates andsuperimposed controls Whenever and wherever required.

A still further object of the invention is to provide a novel allelectric, substantially contactless, A. C. steering system for dirigiblecraft.

Another object is to provide an improved and novel all electricautomatic pilot providing control about three axes.

A further object is to provide a novel automatic threeaxes-of-controlpilot having a rate control superimposed on each axis.

Another object is to provide an automatic pilot for dirigible craftwherein an electric servomotor is energized 'in response to a signalgenerated as a result of a craft departure from a prescribed position tooperate a control surface, a follow-back signal being generated as aresult of the operation of the surface to modify operation of PatentedNov. 27, 1956 the motor in accordance therewith, and a rate s'i'galbeing generated in proportion to the crafts angular velocity developedduring craft departure from its prescribed position to add to thedisplacement signal and oppose the follow-back signal so that thecontrol surface is applied more rapidly on the outward swing, a pointbeing reached where the follow-back signal is equal and opposite to thedisplacement and rate signals to stop the motor and control surface,whereupon the craft returns to its prescribed position. On return, therate signal is reversed to oppose the displacement signal, but adds tothe follow-back signal, whereby the craft is prevented from overswingingits prescribed position once it attains that position, a reverseoperation being applied to the control surface prior to the craftsreturn to its prescribed position to provide a braking action thereon.

A further object is to provide a novel automatic pilot having adirection trim control which may be operated to develop any amount ofchange in heading desired with the automatic pilot engaged and withoutdisconnecting any of the component units from the system, the craftassuming straight flight once the new heading has been attained.

Another object is to provide a novel automatic pilot having an automaticturn control whereby any desired rate of turn may be set in, bank andpitch signals being automatically developed for the rate of turn calledfor.

The above and other objects and advantages of the present invention willappear more fully hereinafter from a consideration of the detaileddescription which follows, taken together with the accompanying drawingwherein one embodiment of the invention is illustrated. It is to beexpressly understood, however, that the drawing is for the purpose ofillustration and description only, and is not designed as a definitionof the limits of the invention.

The single figure of the drawing is a diagrammatic illustration of thenovel automatic steering system of the present invention.

The novel automatic navigation control system comprising the subjectmatter of the present invention embodies a master instrument from whichdisplacement, bank and pitch signals are available for controlling thecraft in heading, as well as in position about its transverse andlongitudinal axes. Repeater systems are interposed in the directiondisplacement channel whereby a change in heading of any desired amountmay be pre-set with the system engaged by injecting an artificialdisplacement signal into one of the repeaters, the craft changingheading until such time as the main displacement signal catches up withand corresponds to the pre-set signal whereupon straight llight isassumed by the craft on the new heading. Furthermore, an automatic turnprovision is made whereby any desired steady rate of turn may be imposedupon the craft, the proper direction displacement, bank and pitchsignals for the predetermined rate of turn being automatically developedwithout imposing any positive load upon the master instrument normallycontrolling such functions.

Referring now to the single figure of the drawing for a more detaileddescription of the present invention, a master instrument l@ is thereshown having a magnetic eld pick-up device in the form of a gyrostabilized earth inductor compass. The pick-up device comprises atriangular element 11, having laminated legs 12, 13 and 14, each havingwound thereon exciting windings 15, 16 and 17, each of the windingsbeing divided into two coils, each pair of coils surrounding a relatedlaminated leg and being connected in series opposed relation. Thewindings are energized from a suitable source of alternating currentsuch, for example, as source 18. The secondary of device 11 comprises adelta connected coil 19 having three taps 20, 21 and 22 which connect byway of Suitable leads 23 with a three phase wound Vstator 24 of aninductive coupling Vdevice 25 mounted within a master indicator shown.generally by vthe reference chara'cterz.

The theory and operation of the magnetic field pick-up device or earthinductor compass is described in greater detail in copending applicationSerial No. 445,102', filed May 29, 1942 and now matured into Patent No.2,716,- '942, granted June 14, 1955, to lohn F. Emerson. For presentpurposes it is only necessary to point out that each leg 12,'13 and 14is saturated and de-saturated twice for every cycle of the excitinglcurrent flowing within primary windings 15, 16 and 17. Thus, the fluxthreading each leg, Y'due to the earths magnetic field, is expelled froma'n'd refenters each leg twice for each cycle of the excitingcurr'eztt.V Since each pair of the coils of the primary windings 15, 16and 17 of each legare wound in series opposed relation no effect isinduced on secondary coil 19 by the exciting current itself. Except whenthe exciting current has attained a substantially maximum value, eitherpositiveV or negative, the earths magnetic eld `is free to traverseeachleg. As a result of the earths field voltages are induced at the threetaps 20, 21 and 22 of secondary coil 19 differing and dependent in valueon the direction in which the pick-up element 'is positioned withreference tothe earths magnetic field. The magnetic field pick-updevice, therefore operates as an earth inductor compass in that forevery deviation from'a prescribed course the induced voltages at thethree taps of the secondary 19 will vary in accordance with deviation.

In order to provide a compass in which turning and acceleration errorsare, Vfor all practical purposes, eliminated so that the tendency of thecompass to oscillate or overswing is thereby prevented, element 11 issecurely fastened to a rotor casing 27 of a three-degree-of-freedomgyroscope having an electrically driven rotor, not shown, provided withvertical spin axis, mounted within casing 27 which supports theV rotorfor oscillation about a first horizontal axis within a gimbal ring 28 bywayof trunnions 29, the gimbal, in turn, being mounted for oscillationabout a Ysecond horizontal axis, perpendicular to trunnions 29, within arigid support carriedby instrument Y10, by means of outer trunnions 30.A suitable erection device may be provided for Ymaintaining the rotorspin axis normally vertical as well as a caging apparatus for cagingand/or uncaging the gyro whenever desired.

In addition to stabilizing the earth inductor compass,

Y the gyroscope is also provided with band and pitch talleoffs in theform of inductive devices 31 and 32, one of which comprises a threephase wound stator 33 having inductively coupled therewith a Vwoundrotor 34 which is movable with t'runnion 30, for example, and 'the otherof which comprises a three phase wound stator 35 having inductivelycoupled therewith a wound Vrotor'36 which is movable with trunnions 29.Both rotors 34 and 36 are tapped to a common conductor 37 forenergization by Vsource 18.' `In practice take-offs 31 and 32 aremounted directly on the gyroscope, take-off 31 being on'the bank axisand take-off 32 on the pitch axis, so that the three principalcontrol'signals are derived from a single master instrument.rangementare obvious, for example, the weight of the Vwhole system isreduced in that where previously at least Y two 'igyroscopes wererequired, i.e., 'a directional and arti- 'eiall horizon gyroscope, thepresent system requires only :one 'gyroscope Moreover, the principalcontrols are concentrated in a singlev casing whereby the device issimple to service and anyV difficulties Yrapidly corrected.

For a condition of equilibrium, i.e., with, the craft on a given:heading and with all controls centralized, the voltages within thethree windings of stator 24 of coupling device 25 of master indicator 26will correspond Yto the voltage at the three taps of secondary coil i9of the pickup device Vand rotors 34 and 36 of take-'ods 31 and 32 willbe at a given position with respect to their related The advantagesarising from such an ar-V fect on the Vrotor winding. As soon, however,as the craftV deviates from a prescribed heading, the voltages at thethree taps of secondary coil 19 will vary causing a variation in thevoltages of each of the stator windings. Such change at the statorproducesfan angular change in'the' resultant of the magnetic eld thereatand, since the electrical axis of the rotor winding is no longer normal`to the Vresultant of 'the field at the stator, a signal is inducedwithin rotor winding .38 which is proportional to the angle of craftdeviation from its prescribed'heading.

The electrical signal induced within rotor winding 38 is fed by means ofsuitable conductors 40 into a conven# tional vacuum tube amplifier 41and out therefrom by means of leads 42 to one phase winding 43 of a'twophase induction motor 44, the. second phase winding 45 of Y which iscontinuously energized from source 18 through a conventional frequencydoubler 46. Becauseas has,

been shown, the frequency of the induced currents within secondary 19 istwice the frequency of the exciting current, 'doubler 46 is included toprovide like frequencies in both motor windings` and in addition, asuitable phase shifting network i's embodied within the doubler so that"Y the phases ofthe current within the two motor windingsY will beVsubstantially 90 apart. i

`Llpon energization of motor phase winding 43, -a rotor 471s actuatedwhich carries a shaft 48 having Vapinion 49 thereon meshing through areduction gear system 50 with a driven gear 51 secured to shaft 39 todrive rotor winding 33 to a Vnull position, i. e., a position whereinthe electrical axis of the rotor winding assumes a position normal'tothe new resultant of the stator Vfield at which point the signal inrotor 38 approaches zero and phase winding 43 of motor 44 isde-energized andtheY motor stops.

In order to provide an indication of the Vnewheading or the amount'ofdeviation oi course, an indicating dial 52 is provided which is carriedby a shaft 53,journalled within the master indicator, the dial beingadapted for angular motion relative to a fixed index 54.V Angular motionis imparted to the dial from vrotor shaft 39 .by way of a gear 55fastened to the shaft'and a gear'56 meshing therewith and having ahollow shaft 57 formed there'- with and secured to dial shaft 53.Preferably shaft 57 is sleeved about shaft 53 and connected therewiththrough a compensating mechanism as shownrand described in co-V Ypending application Serial No. 516,488, led December 3l, 1943, andnowPatent No. 2,625,348, granted Janu- J ary 13, 1953, to P. VA. Noxon etal,v kBy observing dial 5.2', the pilot will immediately knowhis'heading.Y VIfV de'- sired the dial indication may be reproduced atseveral remote stations and to this end shaft 53 carries a gear 58for'meshing with aV gear 59 drivably connected'with the magnet rotor 649of an electromagnetic transmitter 61 whose stator winding connects witha similar electromagnetic .receiver at the remote station, such systemfortreproducing motion being essentially the same as thatr shown anddescribed in U. S. Patent No. Y2,342,637, issued February 29, 1944. Y

In .driving rotor 38 of coupling device 25 to a new null in response Vtocraft deviation from course, Y moto-44 also angularly displaces, from anormally null position,

a woundrortor 6,2 relative to Va three phase wound stator of aninductive transmitter device. 63 with which the rotor is inductivelycoupled, the Vrotor winding being con-"f oped at the stator which may beled directly to a'ruddel'V servo system through an amplier to actuatethe rudder. SuchV an arrangement, however, has the one drawback that ifit is desired to set in a displacement signal independently of the earthinductor compass it could not be accomplished without disconnecting thecompass from the system.

To the end that this may be accomplished without the necessity ofdisconnecting the compass from the system, novel provision is madewhereby the variation in voltages developed at the stator of transmitter63 is communicated by way of leads 65 to a three phase wound stator ofan inductive course setter device 66, normally located within a mastercontrol panel (not shown), the latter stator having inductively coupledtherewith a wound rotor 67. The variation in voltages at the stator ofthe course setter develops an angularly movable ux vector relative torotor 67 whereby a signal is induced in the rotor proportional to theamount of craft deviation from a prescribed course.

Wound rotor 67 is mounted for angular motion relative to its woundstator by means of a conventionally journalled shaft 68 which carries aroller 69 thereon for engagement with a transversely movable disc 70supported for rotation by a shaft 71 which is fastened to a bracket 72,the free end of which is secured to a movably mounted bar 73. Inaddition to engaging roller 69, disc 70 also engages an integrating disc74 supported by a shaft 75 driven at a constant speed by a motor 76which is energized from source 18 by way of a lead 77 tapped toconductor 37, disc 70 normally engaging integrating disc 74 at thecenter thereof so that disc 70 is at rest and will not rotate at suchtime.

The signal induced in rotor 67 is communicated to the input of aconventional vacuum tube amplifier 78 by way of a lead 79 to a iirstswitch A having contacts 1 and 2, contact 1 being closed at this point,lead 80 to a second switch B likewise having contacts 1 and 2, contact 1being closed at this point, a resistor S1 and a lead 82, the ampliiieroutput being fed by way of a lead 83 to energize the variable phase 84of a two phase induction motor 85 having a rotor 86, the second phase 87being constantly energized from source 18 by way of a lead 88. Rotor 86is drivably coupled to move bar 73 through a gear 89 meshing with atoothed portion of the bar, the direction of movement of the bar beingdetermined by the phase of the signal fed to the variable phase of motor85.

Motion of bar 73 imparts a transverse movement to disc 70 from thecenter of rotating disc 74 whereupon disc 70 rotates causing angularmotion of roller 69 and shaft 68 whereupon rotor 67 is moved toward itsnew null position, i. e., toward a position wherein its electrical aXiswill assume a position normal to the resultant ux vector at the statorresulting from the displacement signal generated at compass element 11.Bar 73 is also provided with a toothed portion 90 thereon for engagementwith a worm 91 carried by a shaft 92 which supports a wound rotor 93energized from source 18 by means of a lead 94, the rotor beinginductively coupled with a three phase wound stator 95.

Wound rotor 93 is normally at an electrical null with respect to woundstator 95, however, as soon as motor 85 moves bar 73 to displace rotor67 toward its new null position, rotor 93 is displaced relative to itsstator 95 whereby a signal is induced therein, the latter signal beingopposite to the signal induced within rotor 67. Motion of rotor 67toward its new null position decreases the signal therein until a pointis reached where the signal of stator 95 is greater than the signal ofrotor 67 whereupon the stator signal predominates and motor 85 is drivenin a reverse direction moving rotor 93 back toward its original null androtor 67 away from the new null it was attempting to attain. At thispoint disc 70 is moved toward the center of integrating disc 74 so thatmotion of rotor 67 gradually decreases. As rotor 93 approaches its nullthe signal from rotor 67, though diminished, predominates and 6 againreverses operation of motor 85 until rotor` 67 is finally brought to itsnew null position and rotor 93 assumes its original null positionrelative to stator 95. Anti-hunting on the part of the system is thusovercome and an indicating device 96 may be associated with roller 69whose indication will correspond with the indication of masterinstrument 26 when rotor 67 has been brought into its new null position.When the indications of master instrument 26 and instrument 96correspond, the system is in condition to be engaged by the human pilotto automatically control craft direction of flight.

To obtain automatic control of a rudder surface 97, contacts 1 ofswitches A and B are opened and their contacts 2 are closed. Thereafter,any craft deviation from a prescribed course manifests itself in asignal generated by compass element 11, reproduced at the inductivetransmitter device 63 and the stator of course transmitter device 66, acorresponding signal being induced within rotor 67 thereof which is fedby lead 79 through Contact 2 of switch A to the input of a conventionalvacuum tube amplifier 97a the output of which is fed by a lead 98 to thevariable phase 99 of a rudder servo induction motor 100, the secondphase 101 of which is constantly energized from source 18 by means ofleads 102 and 103. Interposed between motor 101 and a rudder actuatingshaft 104 is a normally disengaged clutch 105 provided with an actuatingsolenoid 106 which is connected through a normally open servo switch 107by a lead 108 with a suitable source of direct current (not shown).

For automatic control, switch 107 is closed by the human pilot wherebysolenoid 106 is energized to engage clutch and thereby establish adriving connection between motor 100 and rudder 97. An electricalfollowup is provided between rudder 97 and compass 11 in the form of aninductive follow-back device having a threephase wound stator 109inductively coupled with a wound rotor 110 energized from source 18 byway of leads 37, 77, 88 and leads 111 and 112, the rotor being mountedfor angular motion by shaft 104. Actuation of shaft 104 by motor 100produces angular displacement of wound rotor 110 from a normally nullposition relative to stator 109 whereby a follow-back signal is inducedin the stator and fed by way of a lead 113 into amplier 97a to be theresuperimposed upon the displacement signal developed at rotor 67 in themanner more fully shown in U. S. Patent No. 2,625,348. The follow-backsignal generated in stator 109 is in opposition to the directiondisplacement signal and increases with rudder displacement as a resultof the continued operation of motor 100 until a given point is reached,at which time the signal within stator 109 is exactly equal and oppositeto the direction signal to thereby wash-out the direction signal atwhich time motor 100 is de-energized and rudder 97 has reached anoutward position in proportion to the direction signal.

With rudder 97 in its applied position and motor 100 de-energized, thecraft will begin to return to its predetermined and prescribed course.In doing so, the direction signal generated by the pick-up device 11starts to diminish in value while the follow-back signal of stator 109,being at a maximum, becomes predominating and energizes motor 100 in areverse direction to start bringing the rudder back to `a neutralposition. With reverse operation of motor 100, the signal in stator 109diminishes-as rotor 110 thereof is brought back to its normally nullposition wherein, unless another direction signal is being generated bythe pick-up device, the rudder and the direction signal generating meansare in synchronism. This condition of synchronism is desirably obtainedwithout the provision of mechanical follow-up connections in the natureof cables, for example, between the rudder and the pick-up device.

The control of the rudder by the direction displacement signal alonewill invariably result in oscillations in that the craft, as it Visbrought back on course, tends to overswing, only to be brought back oncourse once more and then overswing in the original direction ofdeparture;

The net result is to causethe craft to weave about its course ratherthan to remain steadily thereon'.

' By impressing upon the directionsignal, anothersignal that isdependent upon the crafts angular velocity or rate of turn, it is atonce possible to controlcraft oscillation whereby dead beat steering andextreme stability under all weather conditions can be obtained. To thisend, a rate of turn gyro is provided whichV comprises an electricallydriven rotor 114 connected by way of lead 88 with source 18 through lead77, the rotor having normally horizontal spin axis and mounted by way oftrunnions 115 within a gimbal ring 116 which, in turn, is mounted by wayof outer trunnions 117 and 118 for oscillation about a second horizontalaxis perpendicular to the spin axis. Suitable resilient members such assprings 119, for example, are connected to trunnion 117 to yieldablyrestrain gyro precession'to a Vrate of turn function as is known in theart.

To generate a signal proportional to the rate of craft turn, asdetermined by the rategyro, an inductive transmitting device 120 isprovided comprising a three phase wound stator and a wound rotor 121inductively `associated therewith, the rotor being connected to lead37for energization by source 18. Rotor 121, moreover, is mounted ontrunnion 118 for angular motion therewith.

The stator of inductive device 120 has a voltage generated ineach of itsthree windings proportional, respectively, to the angular position ofeach of the windings vrelative to rotor 121 and is connected by a lead122 to the input of ampliier 97a. With rotor 121 `in a given nullposition relative to its stator, i. e., a position in which the crafthas no angular velocity, no signal will be fed to the amplifier throughlead 122. As soon, however, as a departure from course occurs and thecraft also develops an angular velocity, rotor 121 is moved angularlyrelative to its stator producing induced voltages within Vthe statorwindings, the signal developed as a result of such a change beingimpressed upon the direction and followback signals within ampliiier97a.

Thus rthree signals, i. e., direction, rate `and follow-back are mixedor added algebraically within the amplifier to control operation ofinductionY motor 1700. With such provision and during an initial craftdisplacement from a prescribed course, the rate signal aids thedirection signal and opposes the follow-back signal so that Vrudder isapplied more rapidly than it would be by the direction signal alone andduring a return to course the rate signal (the crafts angular velocitynow being in an opposite direction) opposes the direction signal butadds with the follow-back signal so that the craft is prevented fromoverswinging from its prescribed' course once it returns thereto. Thisis in the nature of an anticipatory control which acts to give therudder a slight deflection in an opposite direction when it approacheson course so that it is braked to remain on such course. that the staticrudder position by the foregoing provision is made to be algebraicallyproportional to the Vsum of the rate and direction signals.

Signals for controlling the craft about its'bank and pitch axesV arederived from take-offs 31 and 32 located on gyro trunnions 29 and 30within master instrument 10. The stator 33 of take-off 31 is connectedby leads 125 toV a three phase wound stator 126' of an' inductive banktrim device having a wound rotor 127 inductively It is thus'apparentcoupled therewith, the rotor being connectedto the input of an ampliiiery128 by way of a lead 129. Rotor V127 is supported upon a shaft 130connected to a'lever 131, the free end of'which is connected to arolleri133 which cooperates with a cam 134 fastened to bar 73 so thatmotion of theY bar in one direction rotates the roller to'angularly iVdisplace shaft 139 and rotor 127 in one direction'and motion of the barin an opposite direction rotatesV the roller to angularly displace shaft130 Vandrotor 1277/Y in an opposite direction.

Stator .35 of theV pitch take-ofi device'.32,',ontliejother Y hand,connects by way of'leads 135 l,with a Vthree phase gyro.

wound stator 136, of a pitch trim device, having a wound lead 139. Rotor137 is supported upona shaft 140 con# nected to'one end of a crank 141whose free end isse-v cured to a Vroller V142 adapted for engaging twooppositely inclined cams 143 and 144 so that motion of the bar in onedirection rotates roller 142 along cam surface 144 to oscillate thecrank about shaft 140 as a pivot and, therefore, rotor 137 in onedirection while motion of theY bar in an opposite direction rotatesroller 142 along' cam surface 143 to oscillate the crank as well asrotor.137 in the same direction, the arrangement being such that motionofr bar 73 inV either direction produces Iangular displacement of rotor137 in one direction only.

Three phase wound stators 126 and'136 of the bank and pitch trim devicesare actually repeaters for any bankL and pitch signals generated attake-offs 31 and 32 at the A displacement of the craft in pitch and`bankproduces relative motion of wound rotors 34 and 36 with respect to theirrelated stators 33 Vand 35 whereby unbalanced voltages are developed Vatthe stator windings which are communicated to stator windings 126 and136.`

Due to such unbalance in stator windings 126'and 136, the electricalaxis of rotors 127 and 137 will be no longer normal to the resultant ofthe two fields at thestators so that signals will be induced Yin each ofthe rotors proportional to the bank and pitch of the craft. The twosignals are amplified within ampliiiers 128 and 1387and'the outputsthereof are fed by leads 145 and 146 to the variable phases 147 and 148,respectively, of aileron and,

elevator servo induction motors149 and 150,`the second phase 151 ofmotor 149 being constantly energized from source 18Ythrough leads 102,103 and a lead 152, and the Y second phase 153 of motor 175) beingconstantly energized fromY source 18 through leadsY 102, 103 vand a lead154.- Y interposed between motors 149 and 150 and their re-l spectiveaileron and elevator actuating shafts155 and 156 areV normallydisengaged clutches 157 and 158, each of which is provided withactuating Vsolenoids 159, 160, the. solenoids being connected throughnormally open switches 161 and 162 by way of leads 163 and 164 with asuitable source of direct current (not shown). *Y

Y Beforeswitchesll and 162 are closed to cause engage- 'Y ment ofclutches 157 and 158 to establish a drivable connection between motors149l and 1,50 and their respective Y control surfaces 165 and 166, itshould be determined as to whether or not a condition of synchronismexists between the control system and the control surfaces. For example,the-ailerons may be in a normally centralized position but a bank signalmay exist within rotor127 and at the output of amplifier 128 or theremay be no signal at the rotor but theV ailerons may be displaced. Ineither case motors 149 and 150 would be running as a result ofthe'signals due to bank and pitch or tothe displaced survfaces so Vthatclosing of switch 161, for example, would develop severe jolts on thesystem and the craft. Y K

`Connected across the outputs of amplifiers 128 and 138 aresynchronization indicators 167 and 168,1which may be in the form ofleft-right indicators, and if the craft is banked or tilted about itstransverse axis even though will show the'existence ofthe bank and pitchconditions.

In order to eliminate the bankand pitch signals, vstators,

126 and 136 ofethe bank and pit-ch -trim devices are mounted forangularl motion rela-tive'to wound rotors127 and 137 by way of bank andpitch trim knobs 169and 170. Theseeknobs may be turned toangularlyfdisplace their respective stators 126 and 136until'theresultants of the magnetic fields therein assume'normalpositions vrelative to the electrical axis of rotors 127 Vand 137atwhich vtime no signals are induced in either of the rotors andindicators V167 and 168 indicate a nobank and Yno'pitch condition. Y. Y

If, Von the other hand, no bank orY pitch signals exist in rotors 127and 137 but ailerons 165 and elevators 166 are displaced from acentralized position such condition will be registered upon indicators167 and 168, the reason being that inductive follow-back devices areprovided cornprising three phase wound stators 171 and 172, each ofwhich is inductively associated with a related Wound rotor 173 and 174,the rotors being tapped to lead 111 by way of leads 175 and 176 forenergization from source 18. Rotor 173 is mounted for angular movementwith shaft 155 relative to stator 171 and is at an electrical null withrespect to its stators when ailerons 165 are in a centralized position.lf the ailerons are deflected from a central position, rotor 173 isdisplaced to a position other than a null position at which time asignal is induced in stator windings 171` and fed therefrom by a lead177 to amplifier 128 where indicator 167 registers such unbalance.

Rotor 174 of the elevator follow-back device, on the other hand ismounted for angular movement with shaft 156 and is at an electrical nullwith respect to its stator when elevator 166 is in a centralizedposition. lf the elevators are deected from a central position, rotor174 is displaced to a position other than a null position at which timea signal is induced in the stator windings 172 and fed therefrom by alead 178 to amplifier 138 where indicator 168 registers such unbalance.

The human pilot may then operate the aileron and elevator controlsurfaces manually until they are centralized whereupon rotors 173 and174 return to their null position so that the signals at stators 171 and172 drop to zero and indicators 167 and 168 show this condition. Thesystem is now in synchronism with the control surfaces and switches 161`and 162 may be operated to connect servo motors 149 and 150 with theirrespective control surfaces 165 and 166. Thereafter, any craftdisplacement in bank or pitch will result in signals induced in bank andpitch take-ois'31 and 32 which are also induced within rotors 127 and137 and amplified within amplifiers 128 and 138 Vto energize variablephases 147 and 148 of motors 149 and 158. The motors, being thusenergized, drive ailerons 165 and elevators 166 from their centralposition and simultaneously therewith rotors 173 and 174 of thefollow-back devices are displaced from their electrical nulls relativeto stators 171 and 172 whereby follow-back signals are generated in thestators and fed to their respective amplifiers to be there superimposedupon the bank and pitch signals. These follow-back signals ind-ucedwithin statorsY 171 and 172 are in opposition to the bank and pitchsignals and increase with aileron and elevator displacement as a resultof the continued operation of motors 149 and 150 until a given point isreached, at which time the signals induced in stators 171 and 172 areexactly equal and opposite to the bank and pitch signals at which timemotors 149 and 150 are de-energized and the ailerons and elevators havereached an outward position proportional to the bank and pitch signa-ls.

With ailerons 165 and elevators 166 in their applied positions andmotors 149 and 150 de-energized, the craft will begin to return to acentralized position. In doing so the bank and pitch signals attake-offs 31 and 32 diminish in value while the follow-back signals ofstators 171 and 172, being at maximum, become predominating and energizemotors 149 and 150 in a reverse direction to start bringing the aileronsand elevators back to their neutral positions wherein the controlsurfaces and the bank and pitch generating means are synchronized. As inthe case of the direction control channel, the condition of synchronismis obtained without the use of mechanical follow-up connections such ascables between the ailerons and elevators and the bank and pitchcontrols.

By impressing upon the bank and pitch signals, another signal which isdependent upon the crafts angular velocity or rate of turn developedduring the bank and pitch or climb of the craft, it is possible tocontrol oscillavtion about the bank and pitch axis which might otherwiseoccur. To this end, therefore, rate of turn gyros are provided, eachcomprising electrically driven rotors 179 and 180 connected by way ofleads 181 and 182 with source 1S through lead 37, rotor 179 having anormally vertical spin axis and rotor 1813 having a normally horizontalspin axis displaced from the position of the spin axis of rotor 114 ofthe rate gyro in the direction channel, rotor 179 being mounted by wayof trunnions 183 within gimbal ring 184 which, in turn, is mounted byway of outer trunnions 185, 186, for oscillation about a horizontal axisparallel with the crafts longitudinal axis and rotor being mounted byway of trunnions 187 within a gimbal ring 188 which is mounted by way ofouter trunnions 189, 190, for oscillation about a vertical axisperpendicular to the crafts longitudinal axis. Springs 191 and 192 areconnected to trunnions 4and 189, respectively, to yieldably restraingyro precession to a rate of turn function.

In order to generate signals proportional to the rate of the craftsangular velocity developed during craft bank and pitch, inductivetransmitting devices are provided comprising three phase wound stators193 and 194 having industively associated therewith wound rotors 19S and196, the rotors being connected for energization from source 18 by wayof leads 197 and 198 tapped to lead 37. Rotors 195 and 196, moreover,are carried for angular rnc-tion relative to their stators by trunnions186 and 198 and when the craft is centralized about its bank and pitchaxes the two rotors are at an electrical null with respect to theirstators. As soon as craft bank and pitch occurs an angular velocity isdeveloped about the crafts transverse axis as well as about itslongitudinal axis causing rotors 179 and 184B to precess and therebydisplace the rotors relative to their stators 193 and 194 inducing inthe latter signals which are led to the arnplifiers 128 and 138 by wayof leads 199 and 28d' to be there superimposed upon the bank and pitchsignals and the related follow-back signals in the same manner and forthe same purpose as described in connection with the directiondisplacement signal.

Novel provision is made, furthermore, for changing the direc-tion offlight of the craft from one prescribed course to a second andpredetermined course with the automatic pilot engaged and withoutdisconnecting the compass element 11 from the system. To this end, thestator of the course setter device 66 is mounted for angular movementrelative to its wound rotor 67 and to the end that such statordisplacement may be accomplished, a direction trim knob 261 is provided.

Actuation of knob 261 produces angular motion of the course setterstator so that a signal is induced within rotor 67 thereof. The signalis fed from rotor 67 by way of lead 79 to the input of amplifier 97awhereupon variable phase 99 of motor 180 is energized to apply rudderwhereby the craft turns toward its new course an angular amountcorresponding to the amount of change of course set in by knob 261.During the turn a follow-back signal and a rate signal are developed tomodify the operation of motor and rudder 97 in the manner hereinabovedescribed. The craft changes course in a flat turn until such time asthe signal developed from the earths magnetic field by element 11 andreproduced in the stator windings of the inductive transmitter device 63is sufficient to move the resultant of the magnetic field at the statorof the course setter device 66 to a position normal to the electricalaxis of rotor 67 whereupon the induced signal in the rotor diminishes tozero and the craft will have reached its new course. Thereafter, theautomatic pilot maintains the craft on its new cour-se until and unlessknob 281 is again operated.

A further novel and desirable feature of the automatic pilot of thepresent invention is that an automatic turn may be imparted to the craftwithout disconnecting compass element 11 from the system. To this end,the three phase wound stator 93 of the inductive follow-up 'ars/2,059

device is mounted for angular displacement relative to its rotor 93, anautomatic turn control knob 202 being provided to vaccomplish thispurpose. By setting knob 202, a steady rate :of turn of the craft may bedeveloped with the correct bank and pitch signals automatically set infor the given rate of craft turn.

In manually displacing automatic turn knob 202, stator 95 is angularlydisplaced from its normally null position relative to its rotor 93whereupon a signal is induced in the stator and fed by way of a lead 82to amplifier 7S and out therefrom to energize variable phase 84 of motor85 whereupon the motor moves bar 73 in one direction or another,depending upon the direction of the turn set in by knob 202, to displacedisc 70 relative to integrating disc 74 whereby Vwound rotor 67 of thecourse set-ter device 66 is angu'larly displaced from its null positionrelative to its stator, a signal being induced within rotor 67 and fedtherefrom through ampliiier 97a to operate rudder surface 97 and therebyimpart a constant rate of .turn to the craft.

Simultaneously with the displacement of rotor 67 relative t-o its statorby bar 73, the bar, in moving likewise displaces rotors 127 and 137 ofthe bank and pitch trim devices relative to -their respective stators126 and 136 whereby the correct bank and pitch signals are developed tooperate the aileron and elevator surfaces the correct amount for theparticular rate of turn of the craft set in by knob 202, it being notedthat whether the turn be to the left Vor right of a given course upelevator is provided in either case.

Follow-up motor 85, in response to the signal developed at stator 95 bythe turn knob, will continue to move bar 73 until the latter has movedrotor 93 into a new null position relative to stator 95 whereupon thesignal in the latter drops to zero and motor 85 becomes de-energized. Atthis point disc 70 has been ldisplaced from its normal position relativeto integrating disc 74 a sufcient amount so that rotor 67 of the coursesetter device 66 is angularly displaced at a constant rate relative toits stator. Such operation would continue indefinitely because thedisplacement signal developed within rotor 67 will always be ahead ofthe signal communicated to the stator of the course setter device bycompass element 11. Thus an automatic turn control is provided wherebythe craft may be maneuvered into an automatic turn at any desired ratewithout disconnecting the compass element from the system, the turnbeing completed whenever knob 202 is returned manually to a normalposition,

To disengage the automatic steering system of the present invention sothat the human pilot may control the craft manually, contacts 2 ofswitches A and B are opened and contacts 1 thereof closed while servoswitches 107, 161 and 162 are :opened whereupon clutches 105, 157 and15S disconnect the rudder, aileron and elevator surfaces from theirrespective servomotors 100, 149 and 150. For au-tomatic Hight, on theother hand, the human pilot opens contacts 1 of switches A and B andcloses contacts 2 thereof as wel'l as servo switch 107 of the rudderchannel. When indicators 167 and 168 indicate a condition .ofsynchronism, switches 161 and 162 of the aileron and elevator channelsare closed and thereafter, whenever the craft deviates from a prescribedcourse and/ or a predetermined attitude the system is immediatelyeffective to return the craft to its prescribed s course and/orattitude.

Separate amplifiers 97, 128 and 138 have lbeen shown for the direction,bank and pitch channels, however, one

amplier embodying all three channels-may be usedV equally as well, suchamplifier being shown and described in our above-mentioned U. S. PatentNo. 2,625,348. Moreover, the various inductive devices have been shownas having wound stators and wound rotors inductively coupled therewith,however, electromagnetic devices comprising wound stators having unwoundmagnetic rotors inductively coupled therewith off the characterdescribed and claimed in the above referredrto U. S. Patent No.2,342,637 may be used in place thereof. g Y f There has thus beenprovided a novel all electric automatic pilot wherein theprincipal'contro'l signals, i. e., direction, bank and pitch are derivedfrom a single master instrument. Moreover, novel 'provision is 'made fora direction ltrim adjustment whereby the craft, With' the automaticpilot engaged, may be forced .to change course without the necessity ofdisconnecting the compass element 1i from the system. Furthermore, anautomatic turn may be impressed upon the craft whereby upon theoperation of a single knob a steady rate of turn signal is developedtogether with the proper bank and pitch signals required for theparticular rate of turn Ycalled for;

Although but a single embodiment of the inventionhas been illustratedand described in detailfor controlling a mobile craft about all three ofits axes, it is tobeV eX- pressly understood that .the invention is notlimited thereto. Various changes may also be made in therde'sign andarrangement of the parts without Vdeparting from the spirit and scope ofthe invention as the same will now be understood by those skilled in theart. For example, some of the stators of .the inductive devices may betwo phase wound instead of three, or three phase Wound stators may beprovided but only two ofV the phases would be sufficient toperfoirmV.the various func-tions described. For a denition of the limits of thepresent invention reference will be had primarily to the appendedclaims.

We claim:

l. In an automatic pilot for a crafthaving rudder, aileron and elevatorcontrol surfaces thereon for maintaining it on a predetermined courseandin a predetermined attitude, servomotors foreach of saidcontrolsurlfaces, a single and composite master instrument comprising anartificial horizon Vgyroscctpe having a normally vertical spin axis andmounted forfoscillation about two. mutually perpendicular horizontalaxes, directional reference means mounted on said gyro and stabilizedthere- 'by in a substantially horizontal plane for generating a rstsignal in response to departure of said craft from said predeterminedcourse for energizing said rudder motor, and bank and pitch responsivemeans for generating second and third signals in response to departureof said craft from said predetermined attitude for energizing Y saidaileron and elevator motors, said bank responsive means being mounted onone of said mutuallyY perpendicular axes of said gyroscope and saidpitch responsive .means being mounted on the other-of said mutuallyperpendicular axes.

2. In an automatic pilot for a cratt'having-rudder, aileron and elevatorcontrol surfaces thereon for maintaining the craft on a predeterminedcourse and in a predetermined attitude, electric moto-rsiforV each ofsaid control surfaces, a single and composite master instrulmentcomprising an anticial horizonrgyroscopehaving a normally vertical spinaxis and mounted for oscillation about two mutually perpendicularhorizontal axes, directional referencermeans comprising a magnetic eldpickup device supported on and stabilized by'said gyroscope -in asubstantially horizontal plane and disposed in the earths magnetic fieldfor `generating an electric signal in response' to relativedisplacementof Vsaid Ypick-up device with respect to said ea-r'thsmagnetic field to energize said rudder motor, and 'bank and pitchresponsivemeans for generating electric bank and pitch signals inresponse to departure of sai'dcraft from said predetermined attitude forenergizing said aileron and-elevator motors, said bank responsive meansbeing mounted on oneof said mutually perpendicular axes of saidgyroscopeand said pitch retaining the craft on a predetermined course and in apredetermined attitude of bank and pit-ch, electric motors for each ofsaid control surfaces, a single and composite master instrumentcomprising an articial horizon gyroscope having normally vertical spinaxis and mounted for oscillation about two mutually penpendicularhorizontal axes, directional reference means comprising a magnetic fieldpick-up device supponte'd on and stabilized by said gyrosco-pe in asubstantially horizontal plane and disposed in the earths m-agneticfield for generating an electric signal in response to relativedisplacement of said pickup device with respect to said earths magneticeld to energize said rudder motor, an electrical inductive ydevicemounted on one of said mutually penpendicular horizontal axes andresponsive to departure of said craft from said predetermined attitudein bank for generating an electric bank signal to energize said aileronmotor, an'd a second electrical inductive device mounted on the otheror" said mutually penpendicular axes and responsive to departure of saidcraft from said predetermined attitude in pitch for generating anelectric pitch signal to energize said elevator motor.

4. ln an automatic pilot for a craft having rudder, aileron and elevatorcontrol surfaces thereon for maintaining it on a predetermined courseand in a predetermined attitude, servomotors for -actuating each of saidcontrol surfaces, a single and composite master instrument comprising anartificial horizon gyroscope having a normally vertical spin axis andmounted for oscillation about two mutually perpendicular horizont-a1axes, directional reference means mounted on said gyro and stabilizedthereby in a substantially horizontal plane for generating a firstsignal in response to departure of said craft from said predeterminedcourse for energizing said rudder motor, bank and pitch responsive meansfor generating second and third signals in response to departure of Saidcraft from said predetermined attitude for energizing said aileron andelevator motors, said bank responsive means being mountedl on one ofsaid mutually perpendicular axes of said gyroscope and said pitchresponsive means being mounted on the other of said mutuallyperpendicular axes, and means permanently connected for operation bysaid surfaces in response to the actuation of said surfaces by saidmotors for generating direction, bank and pitch follow-up signals formodifying said lirst, second and third signals.

5. In an automatic pilot for a craft having rudder, aileron, andelevator control surfaces thereon for maintaining it on a predeterminedcourse and in a predetermined attitude, servomotors for actuating eachof said control surfaces, a single and composite master instrumentcomprising an artificial horizon gyroscope having a normally verticalspin axis and mounted for oscillation about two mutually perpendicularhorizontal axes, directional reference means mounted on said gyro andstabilized thereby in a substantially horizontal plane for generating afirst signal in response to departure of said craft from saidpredetermined Acourse for energizing said rudder motor, bank and pitchresponsive means for generating second and third signals in response todeparture of said craft from said predetermined attitude for energizingsaid aileron and elevator motors, said bank responsive means beingmounted on one of said mutually perpendicular axes of said gyroscope andsaid pitch responsive means being mounted on the other of said mutuallyperpendicular axes, and electrical inductive devices permanentlyconnected with said surfaces and operable in response to the actuationof said surfaces by said motors for generating direction, bank and pitchfollow-up signals for modifying said direction, bank and pitch signals.

References Cited in the file of this patent UNITED STATES PATENTS2,240,680 Stuart May 6, 1941 2,383,461 Esval Aug. 28, 1945 2,410,468 VanAuken Nov. 5, 1946 2,415,430 Frische Feb. 11, 1947

